Digital three-dimensional manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital data model. Three-dimensional printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling. Fused Filament Fabrication (FFF) printing, for example, is an additive process in which one or more material applicators extrude polymer filament to form successive layers of material on a substrate in different shapes. In some embodiments, the polymer filament includes fillers, such as metal particles or fibers, or the polymer filament comprises a metal wire coated with a polymer.
The polymer filament is typically unwound from a coil and fed into the material applicator to provide material for a layer. As described in further detail below, in the material applicator, the filament is heated to a temperature that increases the pliability of the material, enabling the material to be extruded selectively through a nozzle onto the platform at a controlled rate. The substrate is typically supported on a platform, and one or more material applicators are operatively connected to one or more actuators for controlled movement of the one or more material applicators relative to the platform to produce the layers that form the object. The material applicators are typically moved vertically and horizontally relative to the platform via a numerically controlled mechanism to position the nozzle at x-, y-, and z-dimension coordinates before depositing the material on the substrate. In alternative embodiments, the platform is moved relative to the material applicators.
One process for producing three-dimensional objects with a FFF printing system 10 is illustrated in FIGS. 6A-6D. As shown in FIG. 6A, during a printing operation, at least one material applicator 14 is positioned relative to a member 18 to space the at least one material applicator 14 vertically above the member 18 in the z-dimension by a height H. As the at least one material applicator 14 is driven in the x-dimension relative to the member 18, the at least one material applicator 14 deposits a layer 22 of material 26 having a length L (shown in FIG. 6B) on the member 18.
The material 26 is fed into the at least one material applicator 14 as a filament 38 that is heated by a melter 42 of the at least one material applicator 14. As mentioned above, the melter 42 heats the filament 38 to a temperature that increases the pliability of the polymer of the filament material 26. Typically, the polymer of the filament material 26 is a thermoplastic, which is a material that is pliable above a certain temperature, referred to hereinafter as a “transition temperature,” and acts as a solid below the transition temperature. Furthermore, some thermoplastics have an amorphous crystal structure, which prevents the material from “solidifying,” or forming a crystalline structure, even below the transition temperature.
When the melter 42 heats the thermoplastic polymer of the filament material 26 above the transition temperature, the intermolecular forces of the material 26 weaken, and the material 26 becomes more pliable and less viscous. At this elevated temperature, the material 26 is selectively extrudable and is hereinafter referred to as being “extrudable” or in “an extrudable state.” The melter 42 does not heat the filament 38 to a temperature which causes the material 26 to become completely liquid and run. Instead, the melter 42 heats the filament 38 to a temperature above the transition temperature at which the material 26 is soft and malleable, but not completely liquid. After being heated by the melter 42, the extrudable material 26 is deposited on the member 18 by a nozzle 46 of the at least one material applicator 14. After being deposited by the nozzle 46, the material 26 cools on the member 18 to a temperature below the transition temperature such that the layer 22 becomes less pliable and more viscous and acts as a solid.
As shown in FIG. 6B, after the layer 22 of material 26 is deposited on the member 18, the at least one material applicator 14 is driven in the z-dimension relative to the member 18 to re-position the at least one material applicator 14 at the height H above the layer 22. Re-positioning the at least one material applicator 14 in the z-dimension accommodates the thickness T of the layer 22 atop the member 18 to prevent the at least one material applicator 14 from contacting the layer 22 during subsequent passes in the x-dimension. After re-positioning in the z-dimension, the at least one material applicator 14 is again driven in the x-dimension to deposit another layer 30 of the object 34 on top of the layer 22. The at least one material applicator 14 can be driven in the x-dimension to pass the member 18 in the same direction or in the opposite direction as the previous pass. If the at least one material applicator 14 is driven in the same direction, the at least one material applicator 14 is also re-positioned in the x-dimension before depositing the further layer 30.
As shown in FIGS. 6C and 6D, the at least one material applicator 14 is also driven in the y-dimension in the same manner as described above with respect to the x-dimension. Accordingly, the at least one material applicator 14 also deposits material 26 to define a width W of the object 34 on the member 18. The at least one material applicator 14 can define the width W of the object 34 either by depositing the material 26 on the member 18 in layers with each layer having the width W in the y-dimension (shown in FIG. 6C) or by depositing multiple layers on the member 18 in the x-dimension to make up the width W in the y-dimension (shown in FIG. 6D). In some printing systems, the at least one material applicator 14 can be driven in a direction having components in both the x-dimension and the y-dimension. Since the three-dimensional object printing process is an additive process, material 26 is repeatedly added to the object 34, and the thickness T of the object 34 increases throughout the process. This process can be repeated as many times as necessary to form the object 34.
One issue that arises in the production of three-dimensional objects with a FFF printing system is the possibility of inconsistent material strength throughout the object. In particular, objects may have inconsistent material strength in the height along the z-dimension. This inconsistency may arise due to weak bonding between the layers of material forming the object, resulting in low and inconsistent interlayer strength throughout the object. A printing system that builds the layers with stronger adhesion between layers would be beneficial.